Compositions for planarizing or polishing the surface of a substrate are well known in the art. Polishing slurries typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the slurry composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium.
Glass magnetic-memory disks have been used as computer hard drives for storing data in lap-top and desk-top PCs for many years. In order to increase the storing capability of hard drives, these glass substrates must be planarized before the magnetic layers are deposited on their surfaces. Chemical Mechanical Planarization (CMP) is used to accomplish this task. The glass disks are polished under pressure against the polishing pad with a polishing slurry continuously supplied on the polishing surfaces.
Glass disks used in laptop hard drives are usually polished (CMP) in two steps: first-step polishing and second-step polishing (or fine polishing). The first-step polishing removes bulk substrate materials from the original substrate. A number of scratches and other defects remain on the surface after the first polishing step. The purpose of the second step polishing is to eliminate all surface defects and generate a very smooth surface. The clay and CeO2 abrasive particles contained in the compositions described herein can be used in both polishing steps.
The term “glass” refers to either silicate (SiO2 -based) or borate (B2O3 -based) glasses which differs in the concentration of modifier ions (such as Pb2+, La3+, and the like). Non-limiting examples of “glass” include: glass disks used in laptop computer hard drives, and different silicon oxides used in ILD (interlevel dielectrics) in IC manufacturing.
Conventional polishing compositions typically are not entirely satisfactory at planarizing semiconductor wafers or integrated circuits having alternating layers of conductive metal and insulating material, e.g., silicon dioxide, that require planar surfaces. In particular, polishing slurries can have less than desirable polishing rates, and their use in chemically-mechanically polishing semiconductor surfaces can result in poor surface quality. Because the performance of a semiconductor wafer is directly associated with the planarity of its surface, it is crucial to use a polishing composition that has a high polishing efficiency, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
Ceria (CeO2) particles are the most commonly used abrasive material in glass CMP slurry formulations due to their unique chemical properties under basic conditions. Different sizes and distributions of CeO2 are selected for different glass CMP slurries in order to meet the requirements of polishing rate and surface roughness. Many glass disk suppliers develop their own ceria-based CMP slurries. Most of these companies are Japanese, such as Hoya, Toyo Kohan, and Fujimi.
Since the trend is always to minimize the size of electronic units and maximize the speed and capability of the storing devices, disk manufacturing companies are continuously looking for ways to improve their polishing rate while decreasing surface roughness. From a slurry composition point of view, one way to accomplish this is to use smaller CeO2 particles to decrease the surface roughness and add chemical additives to enhance the rate; another way is to find novel abrasives.
There have been many attempts to improve the polishing efficiency and uniformity of conventional polishing agents, while minimizing defects in the polished surface and damage to underlying structures or topography. For example, U.S. Pat. No. 5,340,370 describes a polishing composition comprising an abrasive, an oxidizing agent, and water, which purportedly yields an improved removal rate and polishing efficiency. Similarly, U.S. Pat. No. 5,622,525 describes a polishing composition comprising colloidal silica having an average particle size of 20–50 nm, a chemical activator, and demineralized water.
U.S. Pat. No. 5,958,794 ('794) discloses fixed abrasive polishing pads that can perform the CMP function without an abrasive slurry because of the abrasive quality of the pad itself. The '794 patent also discloses the use of very dilute abrasive slurries containing less than 1% particulate abrasive particles. The '794 patent also discloses using abrasive slurries that contain extremely fine abrasive particles, preferably less than 0.1 μm, particularly ceria particles having a particle size of 0.02 μm to 2 μm, having an average particle size less than 1,000 Å, preferably less than 500 Å, more preferably less than 250 Å.
A need remains, however, for compositions and methods that will exhibit desirable planarization efficiency, uniformity, and removal rate during the polishing and planarization of substrates, particularly glass and/or semiconductor wafer surfaces, while minimizing defects, such as surface imperfections.
Ranges may be expressed herein as from “about” or “approximately” one particular value and/or to “about” or “approximately” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment.